1. Field of the Invention
The present invention relates to a dandy roll useful in producing paper having a twill weave wiremark pattern.
2. Description of Prior Art
In papermaking, watermarks are conventionally formed by contacting the paper stock while it is still damp with a dandy roll having raised and/or recessed areas on the surface. An opaque mark known as a "shaded mark" is formed on the paper in areas contacting the recesses on the surface of the dandy roll and is the result of pulp fibers accumulating in the recesses as the paper stock travels under the dandy roll on the papermaking machine. Translucent marks, known as "wire marks," are formed in the paper in areas contacting the raised areas on the surface of the dandy roll. These marks are the result of the raised surface of the roll displacing the fibers in the stock resulting in areas in which the fibers are less concentrated and the paper is more translucent.
It is conventional in the art to form shaded marks by depressing the surface of the wire screen forming the dandy roll and to form wire marks by soldering wire segments, known as electro wires, to the surface of the dandy roll screen. See, for example, U.S. Pat. No. 353,666 to Z. Crane, Jr. (1886) and U.S. Pat. No. 1,571,715 to Fearing (1926). It has also been known to watermark paper by altering the drainage rate of the Fourdrinier screen by modifying the weave in the screen such as by using larger gauge wire to form the screen or by omitting a wire from the screen altogether. See, for example, U.S. Pat. No. 1,616,222 to Harrigan (1927).
In a previous patent to Waters, U.S. Pat. No. 4,526,652, a papermaking process is disclosed wherein paper bearing the look of an oxford cloth weave is produced. The oxford cloth simulation is achieved by positioning narrow pockets and electrowires along the circumferential and longitudinal axis of a plain weave dandy roll screen. While the oxford cloth weave is a desirable effect, other aesthetic effects are also desirable.
By departing from the plain weave dandy roll screen in favor of a twill weave screen, a different aesthetic effect can be achieved. More specifically, the twill weave screen of the present invention imparts more of a "box-like" effect than that of the plain weave dandy roll screen.